In many integrated circuits (ICs) fabricated using a manufacturing process such as a dual-oxide, complementary metal oxide semiconductor (CMOS) process, there is at least one circuit whose components are built within or formed on a thin oxide portion of a substrate and, thereby, comprise one or more thin oxide devices. Such circuits are referred to herein as “thin oxide load circuits” or simply “thin oxide circuits.” Thin oxide devices have higher intrinsic gain than do thick oxide devices (i.e., devices formed in a thick oxide portion of the substrate). However, the thin oxide devices cannot withstand as high of a voltage without damage, as can the thick oxide devices. One consideration is voltage swings of the drain-to-source voltage at a current source transistor that provides a source/drain voltage to one or more thin oxide transistors. This is because too high of a gate-to-source/drain voltage can easily damage these thin oxide transistors. To prevent such damage, an IC containing one or more thin oxide devices should also contain suitable over voltage protection for the thin oxide devices.
The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.